a science-based resource on coffee, caffeine, and health

Many independent studies have associated regular coffee consumption with a significant reduction in the risk of type 2 diabetes - increasing with the volume of coffee consumed (within reason).

Researchers at Harvard University studied125,000 men and women whose health they had been following for 12-18 years. The results showed that women who drink more than six cups of coffee per day reduced their risk for developing type 2 diabetes by almost 30%.

Decaffeinated coffee was associated with a lesser, but significant risk reduction. This suggests that "a component of coffee independent of caffeine, perhaps antioxidants found in both regular coffee and decaf, is responsible for the decrease in type 2 diabetes risk." [Source]

A subsequent 2014 Harvard study found that those who decreased their coffee consumption by more than a cup per day increased their type 2 diabetes risk by 17%.

The same year, scientists at the University of Minnesota in Minneapolis issued findings that coffee offers significant type 2-diabetes risk reduction among postmenopausal women, and in direct proportion to the amount of coffee consumed. Japanese scientists at the University of Nagoya later concluded that coffee appears to reduce pre-diabetic conditions induced by a high-fat diet, hypothesizing that coffee improves insulin sensitivity and glucose tolerance. [Source]

In the Minnesota study, risk reduction was found to be even stronger among those who drank decaffeinated coffee. This lent evidence to the hypothesis that something in coffee other than caffeine is the source of the diabetes risk reduction. Research has pointed to a coffee compound known as chlorogenic acid as a possibility. Other studies have proposed that this and/or other coffee compounds may enhance the body’s natural processing of sugar, positively impacting the glucose uptake system in the liver.

More recently, large review studies have reached similar conclusions. A 2013 meta-analysis (or a study that compiles results from many studies and analyzes them as a whole), covering 1.2 million individuals from the results of 30 independent studies, concluded that coffee may reduce diabetes risk. Higher consumption yielded more reduction – or a positive “dose response.”

Analysis of quantities consumed led the scientists to suggest that incidence of type 2 diabetes was decreased by:

12% for every two cups per day increase of coffee

11% for every 2 cups per day of decaffeinated coffee

14% for every 200 milligrams per day of caffeine

A 2014 meta-analysis, compiling results from 1.1 million people from 30 studies, summarized its analysis as showing a “robust inverse association between coffee consumption and risk of diabetes.” They concluded that people who consume 6 cups of coffee a day may have a 33% lower risk of type 2 diabetes.

More research is needed to understand how coffee may reduce the risk of type 2 diabetes. Scientists suggest that is association may be connected to chlorogenic acid, one of the antioxidants found in coffee.